As already known in the art, systems constituted by blades, which are widely used since many years ago and, which due to the low cost are employed in industry in general, have low yield and may not operate at high speeds or under high pressures; therefore, several modifications and improvements have been carried out in order to solve these disadvantages which are still a concern in the art.
The first problem resides in the shape and in the way of mounting of the blades. If blades are not fixed, they are withdrawn by centrifugal forces when turning the rotor shaft, since blades are mounted inside this shaft, this action and the fact that blades are loose give rise to the continuous bending or swinging thereof, causing flow rate and pressure losses. This problem is in part solved by increasing the length of the blades, which in turn causes enlargement of pump dimensions.
If, instead of using a cylinder displaced with respect to the center of the rotor shaft, a combined cylinder is used, in order to increase the flow rate of the pump, problems are increased since combined cylinders are those having shapes other than cylindrical, which are the combination of two cylinders or the like, two ovals or the like, and, in these cases, additional problems arise since blades should slide over different or uneven surfaces, thus producing the jump of the blades and deformation thereof. In these cases grease or viscous fluids may not be used since they stick the blades inside the rotor shaft and delay outlet of fluids, causing the rotor shaft to rotate without producing any pumping action.
In order to overcome the above disadvantage, springs of varied forms and types have been used; in this case combined cylinders may not be used since springs driving the blades are quickly subject to fatigue and, in the case of a displaced cylinder, rotational speed of the pump should be reduced and the volumetric cylinder capacity under which these pumps may work should also be reduced, in order to maintain at a minimum the compression and expansion of the springs; in spite of this, after a certain working period has elapsed, springs are subject to fatigue and thus break, the blades being released thus bumping and damaging, while the wastes of broken springs damage the rotor shaft.
Also, there are systems allowing the control of the blades; these are based on the use of an eccentric housed inside the rotor shaft, this eccentric has the same shape of the cylinder, whether a displaced or combined cylinder, and by means of different kinds of modifications and adapting techniques, the effect is attained of the blades rotating as per the cylinder contour; to this end, blades have at one of their ends a connecting rod head connected on said eccentric. This makes that when the rotor shaft rotates the blades copy the shape of the eccentric and may operate exactly in accordance with the cylinder contour. In such cases, the blades make two movements, one alternating movement, entering and exiting from the rotor shaft, and a swinging movement, since they are mounted on an eccentric and, therefore, they should accommodate different positions; this means that each blade should be mounted on swinging cylindrical bushes, that all the parts should fit precisely inside the rotor shaft, thus making these pumps of great volume and cost and, in spite of the precision demanded by their construction and since blades contact the cylinder, wearing of both parts is produced, leaving a space or gap between both parts. Since this is a rigid system for control and guidance of blades, the latter may not compensate such wearing, thus leaving a space between the front of the blades and the cylinder, through which the fluid being pumped exhausts.
Another alternative to overcome the problem of controlling and guiding the blades is to include two pins, one at each side of the blades and at the rear part of the blades; such pins are provided with rollers rotating within a groove made within each of the covers. This groove has the same shape than that selected for the cylinder contour and in this way, upon rotation of the rotor shaft, blades also rotate and the pins copy the shape of the groove. In this case the problems are the same as those of the former alternative, namely the front of the blades wears and a space is left between the blades and the cylinder; and since this system is also rigid, blades may not compensate such wear, which causes fluid losses; further, the space or gap existing between the pins and the roller and the roller and the groove into which they are housed, cause bumping of the equipment and, due to the noise produced, they may not operate at high speeds, since the pins are continuously subject to breakage.
A further disadvantage is that all these devices comprised by blades may not operate under high pressure and that in spite of all the improvements and modifications carried out thereon, this was not attained. This is due to the fact that, when the rotor shaft rotates, the blades, being mounted on said shaft, rotate at the same time, subscribing a circumference, but when the cylinder is displaced, namely the center of the cylinder is displaced with respect to the center of the rotor shaft, blades bear on one of their edges instead of bearing on their front, leaving the other edge uncovered, which gives rise to the accumulation of compressed fluids between the blades and the cylinder, which force the blades to separate from the cylinder. These disadvantages are even worse when combined cylinders are used since, although larger flow rates are obtained, the differences between the center of these cylinders and the rotor center are larger and the blades operate almost in all their travel bearing on their edges.